Tooling lugs, located in the outer side wall of turbine nozzles, are a pair of handles with two holes. The function of the holes in the tooling lugs is to connect with the pins in the fixture to hold the nozzle for machining. During machining, a datum plane is used as a reference surface to locate all of the other positions. The tolerance between the tooling lugs and datum plane is very important, because it is directly related to the other machining tolerances and to the part assembly.
When the position or the diameter of a hole of a tooling lug is outside of a predetermined tolerance, the hole is conventionally plugged and re-drilled. The predetermined tolerance may be less than about 2.5 mm (about 0.10″). Conventionally, the hole is plugged by welding, but this may cause distortion or micro-cracking in the superalloy material of the tooling lug.
Brazing is a process of filling a void space within a metal item or between two or more metal items. A filler braze metal material melts and flows into a joint between the two metal items or into a crack or gap within a metal item. The filler braze metal material has a lower melting point than the metal items such that the metal items do not melt during the brazing process. The filler braze metal material ideally flows into the joint, crack, or gap by capillary action. The filler metal is heated to slightly above its melting (liquidus) temperature in a suitable atmosphere, usually in an inert atmosphere environment or in a vacuum furnace, to melt and flow, and then cools to fill the crack or gap or join the two metal items together. Brazing is capable of joining the same or different metals with considerable strength.